Cytokines are soluble, small proteins that mediate a variety of biological effects, including the regulation of the growth and differentiation of many cell types (see, for example, Arai et al., Annu. Rev. Biochem. 59:783 (1990); Mosmann, Curr. Opin. Immunol. 3:311 (1991); Paul and Seder, Cell 76:241 (1994)). Proteins that constitute the cytokine group include interleukins, interferons, colony stimulating factors, tumor necrosis factors, and other regulatory molecules. For example, human interleukin-17 is a cytokine which stimulates the expression of interleukin-6, intracellular adhesion molecule 1, interleukin-8, granulocyte macrophage colony-stimulating factor, and prostaglandin E2 expression, and plays a role in the preferential maturation of CD34+ hematopoietic precursors into neutrophils (Yao et al., J. Immunol. 155:5483 (1995); Fossiez et al., J. Exp. Med. 183:2593 (1996)).
Receptors that bind cytokines are typically composed of one or more integral membrane proteins that bind the cytokine with high affinity and transduce this binding event to the cell through the cytoplasmic portions of the certain receptor subunits. Cytokine receptors have been grouped into several classes on the basis of similarities in their extracellular ligand binding domains. For example, the receptor chains responsible for binding and/or transducing the effect of interferons are members of the type II cytokine receptor family, based upon a characteristic 200 residue extracellular domain.
Cellular interactions, which occur during an immune response, are regulated by members of several families of cell surface receptors, including the tumor necrosis factor receptor (TNFR) family. The TNFR family consists of a number of integral membrane glycoprotein receptors many of which, in conjunction with their respective ligands, regulate interactions between different hematopoietic cell lineages (see, for example, Cosman, Stem Cells 12:440 (1994); Wajant et al., Cytokine Growth Factor Rev. 10:15 (1999); Yeh et al., Immunol. Rev. 169:283 (1999); Idriss and Naismith, Microsc. Res. Tech. 50:184 (2000)).
One such receptor is TACI, transmembrane activator and CAML-interactor (von Bülow and Bram, Science 228:138 (1997); Bram and von Bülow, U.S. Pat. No. 5,969,102 (1999)). TACI is a membrane bound receptor, which has an extracellular domain containing two cysteine-rich pseudo-repeats, a transmembrane domain and a cytoplasmic domain that interacts with CAML (calcium-modulator and cyclophilin ligand), an integral membrane protein located at intracellular vesicles which is a co-inducer of NF-AT activation when overexpressed in Jurkat cells. TACI is associated with B cells and a subset of T cells. Nucleotide sequences that encode TACI and its corresponding amino acid sequence are provided herein as SEQ ID NOs: 1 and 2, respectively
The TACI receptor binds two members of the tumor necrosis factor (TNF) ligand family. One ligand is variously designated as ZTNF4, “BAFF,” “neutrokine-α,” “BLyS,” “TALL-1,” and “THANK” (Yu et al., international publication No. WO98/18921 (1998), Moore et al., Science 285:269 (1999); Mukhopadhyay et al., J. Biol. Chem. 274:15978 (1999); Schneider et al., J. Exp. Med. 189:1747 (1999); Shu et al., J. Leukoc. Biol. 65:680 (1999)). The amino acid sequence of ZTNF4 is provided as SEQ ID NO:3. The other ligand has been designated as “ZTNF2,” “APRIL” and “TNRF death ligand-1” (Hahne et al., J. Exp. Med. 188:1185 (1998); Kelly et al., Cancer Res. 60:1021 (2000)). The amino acid sequence of ZTNF2 is provided as SEQ ID NO:4. Both ligands are also bound by the B-cell maturation receptor (BCMA) (Gross et al., Nature 404:995 (2000)). The nucleotide and amino acid sequence of BCMA are provided as SEQ ID NO:26 and SEQ ID NO:27, respectively.
The demonstrated in vivo activities of tumor necrosis factor receptors illustrate the clinical potential of soluble forms of the receptor. Soluble forms of the TACI receptor have been generated as immunoglobulin fusion proteins. Initial versions resulted in low-expressing, heterogeneous protein. The heterogeneity was observed at the TACI amino terminus, at the Fc carboxyl terminus, and in the TACI stalk region. A need therefore exists for pharmaceutically useful TACI receptor compositions.